Performance Evaluation of Fixed-Bed Downdraft Gasifier Using Agricultural Residues: Syngas Characterisation, Tar Quantification and Cold Gas Efficiency Analysis

This study investigates the gasification performance of three agricultural residues — rice straw, sugarcane bagasse, and bamboo chips — in a 10 kWth fixed-bed downdraft gasifier under varying equivalence ratios (ER: 0.20–0.40) and reactor temperatures (700–900°C). Proximate and ultimate analyses of the feedstocks were performed as per ASTM standards, and a matrix of 45 experimental runs was conducted to evaluate syngas composition (H₂, CO, CH₄, CO₂, N₂ by volumetric gas chromatography), tar content (gravimetric method, ISO 18160), cold gas efficiency (CGE), and carbon conversion efficiency (CCE). Rice straw at 850°C and ER=0.30 yielded the highest CGE of 63.7%, while tar content was minimised at 900°C across all feedstocks (4.8–6.3 g/Nm³). Lower heating values (LHV) of syngas peaked at ER=0.30 for all feedstocks (5.7–6.1 MJ/Nm³). Sugarcane bagasse exhibited the highest volatile matter content (68.4% db) but produced lower syngas quality due to elevated ash content. The findings provide design recommendations for small-scale decentralised power generation using agricultural residues in rural Chhattisgarh and Uttar Pradesh where grid connectivity is limited.